As the Baltimore metropolitan area sizzled again today in the hot, muggy grip of a stubborn Bermuda high, the National Weather Service predicted that more normal temperatures and lower humidity would return by Sunday.

But the weather service said the previous record high minimum temperature for this date of 80 degrees was broken at 5:30 a.m. when 81 degrees was recorded at Baltimore-Washington International Airport.

Nobody knows the brutality of this type of heat wave better than William Palmisano.

"In my business, in this brutal heat, you need a weak mind and a strong back," said Palmisano, president of IRC Roofing in the 900 block of W. Pratt St.

Palmisano said pouring hot asphalt on a roof "can take the best man out." He said he and his workers consume large quantities of water with lemon and salt tablets, and "I have them knock off work at 11 in the morning.

"The asphalt is heated to about 425 degrees and, combined with the weather's heat and humidity, this work can kill you," said Palmisano.

Weather service forecaster Bill Miller said a system of dry air expected to move into the area by Sunday could remain in the region until Tuesday.

Yesterday's high reached 99 degrees at 3:50 p.m. at the Custom House downtown, demolishing the old record of 97 degrees set in 1987. The airport high reached 98 degrees, topping the old record of 94 degrees set in 1969.

The searing heat, 93 degrees at noon, forced most area school systems to close early yesterday. Baltimore public schools were closed today at 12:30 p.m.

Public schools in Baltimore, Anne Arundel and Caroline counties closed three hours early today, officials said. Parochial schools in the city and Baltimore County ended classes at 12:30 p.m. Public schools in Harford and Carroll counties closed two hours early.

Officials in Howard County said schools would be in session the full day. One school, Gateway School in Clarksville, did close because of no air conditioning.

Anne Arundel schools remained open yesterday, but officials announced in the afternoon they would close three hours early today and cancel all kindergarten classes.

City schools also let out at 12:30 p.m. yesterday. Baltimore County schools closed an hour early, and Harford County sent its students home two hours early.

The heat wave has sent weather records tumbling. This month has seen:

* The hottest May since record-keeping began in Baltimore in 1871. Fred Davis, chief meteorologist at the weather service at BWI, said temperatures downtown in May have averaged 73.3 degrees. The old mark was 71.3 degrees, set in 1986. It has also been the hottest May ever at BWI, breaking the old record set in 1959.

* The greatest number of 90-plus days for May in Baltimore -- nine, counting today. That ties a 21-year-old record downtown and sets another record at the airport.

* The longest run of consecutive 90-plus days in May -- seven days including today.

* The warmest overnight low temperature on record for BWI in May. The low of 74 degrees on Tuesday was a record for May. The previous record was 71 degrees on May 31, 1975. The city low of 76 degrees on Tuesday fell short of the 80-degree record set May 30, 1969.

* The biggest demand for electricity for a May day. The Baltimore Gas and Electric Co. said consumers yesterday drew 5,385 megawatts of electricity at 5 p.m. Art Slusark, a utility spokesman, said BG&E today expected to surpass the all-time peak demand of 5,477 megawatts set last July 9.

City residents in two high-rise apartments for the elderly and disabled have suffered through the sizzling days with the air-conditioning systems broken down. Many complained that the problem has been going on for several days. Repairs on one, Hollander Ridge, are to be completed Tuesday, city housing officials said.

The hot May weather does not necessarily portend an especially hot summer, Davis said. After the three warmest Mays on record, in 1959, 1965 and 1970, the airport experienced one warm summer, one cool summer, and one about normal.

The Maryland Department of the Environment reported that ground-level ozone pollution, which can irritate the lungs and cause chest pains, reached unhealthful levels yesterday afternoon in the Baltimore area for the first time this year and smog was expected to hang over the area today and tomorrow.

The air was unhealthful in Anne Arundel and Harford counties and ozone readings in the city and Baltimore County were just below the unhealthful level yesterday.